(234d) The Use of Oxygen Plasma in Activation of Dendrimer-Derived Rh and Pt Catalysts

In recent years, alternative synthetic routes, based on the use of dendrimers as templating agents, have been applied for the synthesis of supported metal catalysts. Dendrimers are hyper-branched macromolecules with various functional groups and interior voids that can accommodate metal precursors in solution and protect them from aggregation until they are delivered onto the surface of the support. Following deposition on the support, metal nanoparticles remain encapsulated in the dendrimer, which must be removed to render active metal sites available for gas phase reactants. Primarily high temperature treatments have been used for the removal of the dendrimer component in such systems. However, most metals undergo further sintering during such treatments and as a result alternative ways to activate these catalytic materials without affecting metal dispersion could have a substantial impact in this field. In this study we explore an alternative dendrimer removal technique based on the use of high energy particles from an ionized oxygen plasma source. The effect of the plasma treatment on dendrimer-derived Rh/ZrO₂ and Pt/g-Al₂O₃ catalysts has been evaluated by FTIR, XPS, and STEM characterization measurements. The effects of various factors, such as the treatment time, temperature, and the plasma power on the size and structure of the resulting supported metal particles has been examined systematically. The catalytic activity of the resulting materials was also evaluated for the oxidation of CO and the results obtained were compared with similar results collected for analogous samples that underwent high temperature treatments. The results suggest that the plasma treatment examined can be a very effective technique for the removal of the dendrimer component, leading to samples with substantially higher metal dispersions and overall catalytic activity.